DESCRIPTION: This proposal aims to provide further understanding of the interactions between the sympathetic nervous and renin angiotensin systems. The actions of Ang II on the adrenal medulla, at sympathetic nerve endings, and on the brain and sympathetic ganglia will be studied in conscious rabbits. The main focus of the proposal is to determine the mechanisms behind the attenuation of reflex increases in sympathetic activity during blockade of the renin-angiotensin system. Specifically, experiments are designed to: 1) compare effects of converting enzyme inhibitors and Ang II antagonists on the carotid occlusion response; 2) use nephrectomy to assess the importance of the renal renin-angiotensin system; and 3) to determine the site of the interaction between the two systems by evaluating the brain with emphasis on intravertebral route and area postrema, the brain renin-angiotensin system, the adrenal medulla, and sympathetic nerve terminal. The studies are designed to better understand the mechanisms of action of converting enzyme inhibitors and Ang II antagonists and will provide further information on the importance of interactions between the sympathetic nervous and renin-angiotensin systems in the reflex control of pressure.